The jserv.log and OACoreGroup..stderr (where is the number of the JVM) will show errors like:-

Exception in static block of jtf.cache.CacheManager. Stack trace is:
oracle.apps.jtf.base.resources.FrameworkException: IAS Cache initialization failed. The Distributed Caching System failed to initialize on port: 12346. The list of hosts in the distributed caching system is: hostA.domain.com . The port 12346 should be free on each host running the JVMs. The default port 12346 can be overridden using
-Doracle.apps.jtf.cache.IASCacheProvidercacheProvider.port=
at oracle.apps.jtf.cache.IASCacheProvider.init(IASCacheProvider.java:220)
at oracle.apps.jtf.cache.CacheManager.activateCache(CacheManager.java:1444)
at oracle.apps.jtf.cache.CacheManager.initCache(CacheManager.java:752)

java.lang.NoClassDefFoundError
at org.apache.jserv.JServServletManager.load_init(JServServletManager.java:765)
at org.apache.jserv.JServServletManager.loadServlet(JServServletManager.java:659

SOLUTION

Disable Java Caching Mechanism.

Comment out the following line in jserv.properties to disable Java Caching

As a consolidated suite-wide patchset, this RUP includes new features, statutory and regulatory updates, and enhancements for stability, performance, and security.

Release 12.2.7 is cumulative. That means that as well as providing new updates for this release, it also includes updates that were originally made available as one-off patches for earlier 12.2 releases.